EXPERIMENTAL ANALYSIS 



On the basis of a long experience, starting with fractionation experi- 

 ments in 1925 (Fischer133^ which aheady demonstrated that some of 

 the active components of embryo extracts were very labile, Fischer^^ 

 has come to regard 'embryonin' as a true 'growth catalyst'. Many 

 attempts at purification of this fraction have resulted in reduction of 

 its activity, and Fischer has not succeeded in identifying any single 

 chemical entity possessing the embryonin activity. The embryonin 

 fraction, prepared by the method of Hammarsten^^* for isolating 

 nucleoprotein from pancreas, is heterogeneous in character, showing 

 four main and many minor components on electrophoresis (Fischer 

 and AsTRUP'^^). 



In a study of the stimulating effect of embryo extracts on fibroblast 

 cultures, Jacoby et alii^^^ demonstrated that an extract need not be 



Figure 63 Graph showing the relation between the dura- 

 tion of the application of embryo juice to cultures of chick 

 periosteal fibroblasts and the amount of growth which is 

 produced. Ordinates: the aggregate percentage of cells 

 which divide between the loth and 20th hours after the 

 application of the juice. Abscissae: time in Jiours A 40 

 per cent, 6 15 per cent, and C 5 per cent embryo juice. 

 From Jacoby et alii^^^ {By courtesy, J. exp. Biol.). 



present in appreciable amounts during the actual process of cell 

 division. It is required only to initiate a process which, after a latent 

 period of lo to 12 hours, culminates in cell division. Short contact 

 with embryo extract (less than 10 hours) produces only one crop of 

 mitoses (Figure 62), but the number of mitoses is more dependent on 

 the concentration of extract than the time for which it acts (Figure 63). 

 Tompkins et alii^^^ showed that the stimulus to division produced by 

 fresh embryo extract disappeared between 48 and 72 hours. To obtain 



177 



